1. Field
A method for transferring a substrate and a method for fabricating a flexible display by using the same is provided.
2. Description
Recently, the importance of a display as a visual information transfer medium has increased. The trend has been to lower the devices power consumption, increase picture quality and create a thin and light device.
Displays can be divided into a light emission type display, for example, a cathode ray tube (CRT), an electro luminescence (EL), a light emitting diode (LED), a vacuum fluorescent display (VFD), a field emission display (FED), a plasma display panel (PDP), and a non-light emission type display such as liquid crystal display (LCD) that cannot emit light by itself.
A flexible display that cannot be damaged although it is folded or rolled is anticipated to emerge as a new technique in the field of displays.
The flexible display, also called a roller display, is implemented on a thin substrate such as plastic and can be folded or rolled without being damaged. The OLED and LCD, which can be fabricated with a thickness of below 1 mm, are favored over the other types of devices.
Because the OLED emits light by itself, it has a good visibility no matter whether it is in dark or external light is introduced, and can implement high quality video with its fast response speed. The response speed is used as an important reference that determines performance of a mobile display. Currently, the OLED has the fastest response speed among the existing displays. The OLED allows an ultra-thin film designing that make diverse mobile devices slim.
The LCD is a device that displays images by using optical anisotropy. The LCD has excellent visibility, smaller average current consumption and reduced heating, compared with the existing CRT. These advantageous features make the LCD a popular device.
In order to implement a flexible display by using the LCD or the OLED, a plastic substrate or a flexible substrate such as a metal foil is used. In order to transfer the flexible substrate and perform the follow-up process, the plastic substrate is attached on a glass substrate with an adhesive. This bonding process is complicated and a plurality of laminating processes are performed, and thus there is an increased possibility that a defect will occur during productivity.
FIGS. 1A and 1D are perspective view showing the sequential process of a general method for transferring a substrate of a flexible display. The drawings sequentially show the process of attaching a plastic substrate on a glass substrate by using a general bonding technique, transferring it, and performing a follow-up process.
In order to transfer the plastic substrate and perform the follow-up process, a process that attaches the plastic substrate on the glass substrate is performed. FIG. 1A shows an adhesive 40 positioned between the plastic substrate and the glass substrate. Protection films called release papers 41 and 42 are attached on both surfaces of the adhesive 40. Before attaching the adhesive on the glass substrate the lower release paper 42 must be removed.
As shown in FIG. 1B, the lower surface of the adhesive 40, from which the lower release paper 42 has been removed, is attached on an upper surface of the glass substrate 10 through a lamination process. The adhesive 40 is attached on the glass substrate 10 by using a roll 60, and an air bubble should not be generated between the adhesive 40 and the glass substrate 10.
After the adhesive 40 is attached on the glass substrate 10, the upper release paper 41 is removed and the plastic substrate 20 is attached to the upper surface of the adhesive 40.
As shown in FIG. 1C, the plastic substrate 20 is attached on the upper surface of the adhesive 40 through another lamination process.
Because of the number of different processes required to attach the plastic substrate to the glass substrate there is an increased possibility that an air bubble can be generated during the lamination process or a blot can be generated during the process.
The plastic substrate 20 attached on the glass substrate 10 is transferred and a fabrication process is completed through several processes. After fabrication, as shown in FIG. 1D, the plastic substrate 20, is separated from the glass substrate 10.
When separating the plastic substrate 20 from the adhesive 40, attached on the glass substrate 10, several conditions should be satisfied to properly separate the layers. If the adhesive 40 is attached on the front surface of the substrates 10 and 20, the separation process become even more complicated and difficult.
If the separation process is not properly performed, the adhesive 40 may remain on the surface of the plastic substrate 20, and in this case, an additional cleaning process should be performed to remove the remaining adhesive 40.
The plastic substrate is vulnerable to heat and chemicals and thus there are additional restrictions in its processing conditions such as a process temperature when several processes are performed. As the flexible substrate, a thin (about 100 μm) light metal foil substrate, having excellent heat resistance and chemical resistance, can be used in place of the plastic substrate.
When using the metal foil substrate, the same transfer problem as the plastic substrate arises, and when the separation process is performed, the possibility that the metal foil substrate become bent is increased.
Because the surface of the substrate is rough compared with the plastic substrate, an organic insulation film should be additionally formed on the upper surface of the metal foil substrate. This requires additional steps and processes. In addition, an inorganic insulation film should be formed to prevent chemical damage to the upper and lower surface of the metal foil substrate on which the organic insulation film has been formed.